1. Field of the Invention
The present invention relates to ground penetration radars, and more particularly sensors that help guide coal mining and directional drilling machinery.
2. Description of Related Art
The United States energy demands for coal and coal-bed methane are increasing faster than 1.8 percent per year. To meet this demand for energy, production will need to be increased by more than 46 percent by the year 2025. Although energy experts believe that coal is abundant, the facts are quite different. The rate at which the United States is depleting its reserves has been underestimated. In the Raton Coal Basin, the cavitation method of coal-bed methane production has spoiled more than one billion mineable tons of coal—about one year's United States coal production. Extracting five percent of the coal bed methane (CBM) British thermal units (BTU) using high-pressure cavitation spoils 95 percent of the coal BTUs. Elsewhere, the easy-to-mine coal reserves are nearing exhaustion. Future mining will be in thinner, deeper, more geologically complex coal seams and near abandoned mines. For the coal mining industry to keep up with energy demands, a quantum leap forward in mining technology will be needed.
The technical challenges facing future coal miners are significant and well known to mining personnel who have dedicated lifetimes to solving difficult production and safety issues. The National Mining Association (NMA) executives, in a technology road-mapping session sponsored by the United States Department of Energy's (DOE) Mine of the Future program, prioritized technology needed by the industry in future years. The top ten needed technologies included the following:
Coal-cutting-edge sensing for selective mining to minimize out-of-seam dilution and improve run-of-mine coal quality. The Quecreek event added the safety need to prevent mining into abandoned coal mines.
Coal seam beds are undulating geologic structures with complex gradational boundaries. Each ton of coal has one billion square feet of surface area in its matrix, and can entrain 100-1,000 cubic feet of methane. The depositional environment of a coal seam includes microbial processes that feature aerobic and anaerobic bacteria accumulation. The heavy metals are oxidized by the oxygen-rich environment of the upper flood plane and the soluble oxide contaminants are carried by river flow into the reducing environment of the delta-region swamp. The reducing environment (septic conditions) causes sedimentation of the heavy metals near the coal-seam boundary. Thin bounding layers are contaminated with mercury, sulfur, and ash. Leaving this contaminated layer behind improves coal quality and, in some mines, the thin layer is stronger than the weak roof rock. The layer prevents ventilation air from drying and subsequent spalling of the roof rock. The thin layer reduces the potential for a roof fall, especially along the margins of paleochannels. The contamination also decreases the gas flow permeability near the boundary.
Channel samples often confirm that gradational boundary and fire clay layers have high levels of mercury and other heavy metals that contaminate surface water discharged in the methane drilling and production process. Boundary detection requires that sensors be located near the cutting edges of buckets, blades, rotating drums, and bottom-hole assemblies. Real-time detection of mine voids at least twenty feet (6.1 meters) ahead of the coal cutting machine is needed. Because a mining depth of forty feet is common practice with remote-control continuous mining machines, ground-control safety requires roof bolting before mine personnel can advance into a newly developed entry. From an abandoned mine detection safety perspective, the look-ahead radar must be integrated into the cutting drum of a continuous mining machine. If the detection sensors are located far away from the cutting edges, feedback control systems on automated machines and gimbals fail to provide closed-loop control. Full machine automation becomes impracticable.
For void detection ahead of mining, the United States Mine Safety and Health Administration (MSHA) requires horizontal directional drilling in mines operating near abandoned mining complexes. In-mine drilling slows down mining processes because it requires relocating and repositioning a drilling machine. The efficiency of longhole horizontal directional drilling to probe for abandoned mine boundaries increases if the borehole can be maintained within the coal bed. One solution is to adapt radar to find the abandoned mining complexes and operate the radar near the recently cut face. In-mine demonstrations of hand-held commercially available ground-penetrating radar (GPR) have conclusively demonstrated that abandoned mines can be detected.
Radars designed for installation near the cutting edge are not even a close cousin to GPR. Radar operated for this purpose requires intrinsically safe (IS) or flameproof certification from the MSHA Certification and Approval Center in Tridelphia, W. Va. Developing a product that achieves this certification requires a highly qualified design team understanding the technical requirements. The intrinsic safety design requirements are not taught in design engineering curricula. As an example of the time required to certify a complex electronic circuit, the engineering team must work with MSHA in an iterative design process that can involve more than a year to complete. The intrinsically safe battery protections approval cycle requires thirty-six months to complete. The radar must be designed to withstand exceedingly high g force of vibration and shock, while processing data in real time using fast, autonomous algorithms. Because the radar must be “trialed” under realistic mining and drilling conditions, the electronics design must accommodate software reprogramming while the machine in cutting coal or drilling in hydrocarbon reservoirs. This feature is called remote wireless programming while mining or drilling. The software design industry refers to this advanced concept as in-application programming (IAP). The radar must control the mining machine or gimbal in real time. The look-ahead radar design must include self-testing and redundant fail-safe detection.